1. Field of the Invention
This invention relates to a method and apparatus for eccentricity correction in a rolling mill system.
2. Description of the Prior Art
In hot and cold rolling mills the eccentricity of the back-up rolls results in a major problem, in that, if uncorrected this will cause a change in the exit gauge of the product being rolled. As a result of this eccentricity, as the back-up rolls are displaced, they present a variable opening to the workpiece being processed.
Most rolling mills today utilize an automatic gauge control (AGC) which is a vernier trimming control added to the basic mill control system in order to compensate for delivered gauge variations. A mill is initially set up as near as can be predicted, to run a given schedule to produce the desired gauge. The AGC system then takes over while the strip is being rolled to monitor and correct for initial gauge errors as well as those occurring during rolling. The AGC utilizes a roll force signal from a load cell, associated with the rolls to be monitored, as an indication of gauge variation. As the gauge increases, or a harder surface is presented at the roll opening, this causes an increase in the roll separating force. The AGC senses this increase in roll force, and signals for the rectilinear displacement of the rolls in such direction as to increase the roll force further to reestablish the proper gauge. The reverse occurs if the gauge or thickness decreases or softer material is presented to the rolls.
Eccentricity of the back-up rolls produces a periodic increase and decrease in the roll force as the rolls rotate. When eccentricity causes an increase in roll force, without compensation, the AGC would interpret this as an increase in gauge (the opposite is true) or hardness, and signal for an increase in roll force, which compounds the error making it worse than if due to eccentricity alone. The reverse obtains when eccentricity causes a decrease in gauge.
These considerations are well known in the art and various corrective techniques have been offered. It has been proposed to give the AGC a deadband greater than the gauge error caused by the back-up roll eccentricity. Another solution teaches simulating back-up roll eccentricity with a mechanical cam having a contoured surface corresponding to that eccentricity, and then feeding the simulated eccentricity to the AGC as a correction signal.
The closest known prior art to the instant invention is described in U.S. Pat. No. 3,882,705 for "Roll Eccentricity Correction System and Method," by Richard Q. Fox and assigned to the same assignee as the present invention. In this patent, the eccentricity of each back-up roll is measured and recorded during calibration in order to monitor the rotation of these rolls during the rolling process, and to correct the roll force gauge control equation to dynamically compensate for the eccentricity of the rolls.